Composite Ceramic Material and Method for Manufacturing the Same

ABSTRACT

Provided is a composite ceramic material for a fuel cell and a method for manufacturing the same. The composite ceramic material for the fuel cell forms a cored structure where perovskite ceramic particles having a small particle diameter surround lanthanum cobaltite particles having a large particle diameter, and lanthanum cobaltite is added as a starting material in a process of synthesizing the perovskite ceramic particles to be synthesized. The composite ceramic material for the fuel cell described herein improves an electric connection characteristic between a separation plate and a polar plate of the fuel cell, and is chemically and mechanically stable.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a fuel cell, and more particularly, toa composite ceramic material electrically connecting an anode and aseparation plate of a fuel cell, and a method for manufacturing thesame.

(b) Description of the Related Art

Among fuel cells, if a solid oxide fuel cell (SOFC) is described as anexample thereof, the fuel cell is formed of a structure where aplurality of electric generating units formed of a unit cell and aseparation plate are laminated. The unit cell includes an electrolytefilm, an anode (air electrode) disposed on one surface of theelectrolyte film, and a cathode (fuel electrode) disposed on anothersurface of the electrolyte film.

If oxygen is supplied to the anode and hydrogen is supplied to thecathode, oxygen ions generated by a reduction reaction of oxygen at theanode are transported through the electrolyte film to the cathode, andthen reacted with hydrogen supplied to the cathode to generate water. Inthis case, in the course of transporting the electrons generated at thecathode to the anode to be consumed, the electrons flow to an externalcircuit, and the unit cell generates electrical energy by using the flowof electrons.

In the case of the solid oxide fuel cell, since electrical energygenerated by one unit cell has a limitation, generally, a stackstructure where a plurality of unit cells is laminated is formed.

In each unit cell having the stack structure, a separation plateelectrically connecting the anode and the cathode and preventing gasesfrom being mixed is generally used.

Generally, a stainless steel plate is used as the separation plate, theseparation plate provides a gas flow path to the anode (air electrode)and also provides a gas flow path to the cathode (fuel electrode).

One of the methods of improving performance in the solid oxide fuel cellis to reduce electrical resistance of the stack, that is, internalresistance of the fuel cell.

To this end, a constitution where a material having excellent electricconductivity is used as the material of the separation plate and thepolar plate or contact electrical resistance thereof is reduced has beenproposed. An example thereof includes the case where a current collectortransporting current is inserted between the anode and the separationplate and a platinum mesh (Pt mesh) is used as the current collector.Examples of another method include the case where an antioxidant metalmesh is used instead of platinum in order to reduce cost.

However, in the case where the metal material is used as the currentcollector, when the material is exposed to an oxidizing atmosphere overa long period of time, there is a problem in that oxides are formed on asurface thereof to increase resistance of a stack, thus deterioratingperformance of the stack.

Accordingly, it is required that oxides that are stable and exhibitsconductivity even in an oxidizing atmosphere are adopted to ensurestable performance even when a stack is operated over a long period oftime.

A ceramic material having a perovskite structure is known as a contactmaterial electrically connecting the polar plate and the separationplate of the fuel cell.

However, in the case of the perovskite ceramic material, physicalproperties of the material need to be further improved so thatelectrical conductivity is further improved and the material ischemically and mechanically stable.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a compositeceramic material that improves an electric connection between aseparation plate and a polar plate of a fuel cell maintained in anoxidizing atmosphere and is chemically and mechanically stable.

Further, the present invention has been made in an effort to provide amethod for manufacturing a composite ceramic material that improves anelectric connection between a separation plate and a polar plate of afuel cell maintained in an oxidizing atmosphere and is chemically andmechanically stable.

An exemplary embodiment of the present invention provides a compositeceramic material including: fine ABO₃ type perovskite ceramic particlescompositely synthesized with lanthanum cobaltite (LaCoO₃) particleshaving a particle diameter that is larger than a particle diameter ofthe perovskite ceramic particle.

It is preferable that the composite ceramic material form a coredstructure where the perovskite ceramic particles surround the lanthanumcobaltite particles, and that the lanthanum cobaltite be synthesized bybeing added with a starting material in a process of synthesizing theperovskite ceramic particles.

In the composite ceramic material, it is preferable that a ratio of thelanthanum cobaltite be greater than 10 wt % and less than 90 wt %.

Further, in the composite ceramic material, it is preferable that theperovskite ceramic particle be any one of (La,Sr)MnO₃, (La,Sr)CoO₃,(La,Sr) (Co,Fe)O₃, and (La,Ca) (Cr,Co,Cu)O₃, and the particle diameterthereof be 100 nm or less. It is more preferable that a composition ofthe perovskite ceramic be(La_(0.8)Ca_(0.2))(Cr_(0.1)Co_(0.6)Cu_(0.3))O₃.

In addition, in the composite ceramic material, it is preferable that aparticle diameter of the lanthanum cobaltite particle be 0.5 to 5.0 μmand the lanthanum cobaltite particle have a sphere shape.

Another exemplary embodiment of the present invention provides a methodfor manufacturing a composite ceramic material, including: i) adding amixture where citric acid and lanthanum cobaltite powder are mixed witheach other to a nitrate aqueous solution where a plurality of nitratesare dissolved; ii) heating and agitating the aqueous solution to converta reactant from a sol state to a gel state; iii) heating the reactantproduced in the heating and agitating to a temperature of self-ignitionor more of the citric acid to combust the citric acid; and iv)pulverizing chars produced in the combusting the gel and then heattreating and calcining the chars at 700° C. or more.

In the method for manufacturing the composite ceramic material, it ispreferable that a particle diameter of the lanthanum cobaltite powder be0.5 to 5.0 μm, and a ratio of the lanthanum cobaltite added to thenitrate aqueous solution be greater than 10 wt % and less than 90 wt %.

Further, the nitrate aqueous solution is obtained by dissolving at leastone metal nitrate selected from lanthanum nitrate, calcium nitrate,chrome nitrate, cobalt nitrate, copper nitrate, iron nitrate, bismuthnitrate, yttrium nitrate, manganese nitrate, strontium nitrate andnickel nitrate in distilled water to correspond to a composition of aABO₃ perovskite ceramic.

Herein, it is preferable that the ABO₃ perovskite ceramic be any one of(La,Sr)MnO₃, (La,Sr)CoO₃, (La,Sr) (Co,Fe)O₃, and (La,Ca) (Cr,Co,Cu)O₃.It is preferable that a composition of the (La,Ca) (Cr,Co,Cu)O₃ be(La_(0.8)Ca_(0.2))(Cr_(0.1)CO_(0.6)Cu_(0.3))O₃.

In addition, it is preferable that the citric acid be used as acombustible organic material contributing to forming a metal complex andforming ceramic powder by combustion at high temperatures, and thecombustible organic material be any one of glycine nitrate, polyethyleneglycol, urea and ethylenediamine tetraacetate.

Furthermore, the method for manufacturing the composite ceramic materialfor the fuel cell according to the exemplary embodiment of the presentinvention further includes uniformly mixing the calcined powder, acombining material, a dispersion material and a solvent to manufacture aviscous fluid (slurry).

The method for manufacturing the composite ceramic material according tothe exemplary embodiment of the present invention further includesapplying the manufactured viscous fluid on a polar plate or a separationplate of a fuel cell and then sintering the viscous fluid. In this case,it is preferable that the sintering be performed at 600° C. or more for1 hour or more.

Yet another exemplary embodiment of the present invention provides afuel cell including: a polar plate or a separation plate coated with thecomposite ceramic material manufactured by the aforementioned method.

Still another exemplary embodiment of the present invention provides afuel cell including i) a unit cell formed of an electrolyte film, ananode (air electrode) disposed on one surface of the electrolyte film,and a cathode (fuel electrode) disposed on another surface of theelectrolyte film; and ii) a separation plate electrically connecting theanode and the cathode and coated with the composite ceramic material.

According to exemplary embodiments of the present invention, themanufactured composite ceramic material has excellent electricalconductivity at an operation temperature of a fuel cell and exhibits atechnical effect of maintaining a chemically stable state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope picture of a lanthanumcobaltite powder used to manufacture a composite ceramic material for afuel cell according to an exemplary embodiment of the present invention.

FIG. 2 is a picture of the composite ceramic material manufacturedaccording to the exemplary embodiment of the present invention, which istaken by a field emission scanning electron microscope (FESEM).

FIG. 3 is a picture illustrating current-voltage curved line andcurrent-electric power curved line graphs of a solid oxide fuel cell towhich the composite ceramic material manufactured according to theexemplary embodiment of the present invention is applied.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

A composite ceramic material described below is mainly described by asolid oxide fuel cell as an example thereof in the presentspecification, but the present invention is not limited thereto andapplied to all cells using the composite ceramic material.

In the composite ceramic material according to the exemplary embodimentof the present invention, fine ABO₃ perovskite ceramic particles arecompositely formed together with lanthanum cobaltite (LaCoO₃) particleshaving a relatively large particle diameter. Preferably, a so-calledcored structure where the fine ABO₃ perovskite ceramic particlessurround the lanthanum cobaltite particles having a large particlediameter is formed.

The composite ceramic material is manufactured by firstly dissolvingnitrates in water to manufacture a nitrate aqueous solution and thenmixing and heating the nitrate aqueous solution, citric acid andlanthanum cobaltite powder.

Hereinafter, a starting raw material for manufacturing the compositeceramic material according to the exemplary embodiment of the presentinvention will be described.

First, the nitrate aqueous solution is manufactured by dissolving atleast one metal nitrate selected from lanthanum nitrate, calciumnitrate, chrome nitrate, cobalt nitrate, copper nitrate, iron nitrate,bismuth nitrate, yttrium nitrate, manganese nitrate, strontium nitrateand nickel nitrate in distilled water.

In this case, the composition of nitrate dissolved in distilled water isstoichiometrically determined to correspond to the composition of theABO₃ perovskite ceramic. That is, the composition ratio of added metalnitrate is determined according to the composition of the finally formedconductive perovskite ceramic.

Examples of the composition of the finally formed perovskite ceramicinclude (La,Sr)MnO₃, (La,Sr)CoO₃, (La,Sr) (Co,Fe)O₃, (La,Ca)(Cr,Co,Cu)O₃ and the like.

Next, the citric acid that is the starting raw material acts as a ‘fuel’for combustion synthesis. Accordingly, the combustible organic materialcontributing to forming a metal complex such as glycine nitrate,polyethylene glycol, urea and ethylenediamine tetraacetate and formingceramic powder by combustion at high temperatures may be used. Further,the other organic material, for example, ethylenediamine tetraacetatemay be used with citric acid and ammonia water. However, since thecitric acid can act alone as a metal complex forming agent and a fuel,it is preferable to use the citric acid.

The addition ratio of the citric acid is determined according to theratio of cations in the nitrate aqueous solution. In more detail, theoxidizing amount of nitrate and the oxidizing amount of the citric acidare determined to correspond to each other. The oxidizing amount may begenerally an atomic valency of an element, but in the case of a rapidredox reaction, that is, in the case where the ceramic is synthesizedthrough a combustion process, the meaning thereof is slightly changed.

For example, the oxidizing amount of La is +3, the oxidizing amount ofoxygen (O) is −2, that of carbon (C) is +4, and that of hydrogen (H) is+1, but since nitrogen (N) is considered to be inert, the oxidizingamount thereof is 0.

Accordingly, the oxidizing amount of each nitrate is determinedaccording to this method, and the oxidizing amount of the mixture may becalculated according to a molar ratio.

The citric acid having the oxidizing amount of the quantitycorresponding to the quantity of the negative oxidizing amount of thenitrate mixture calculated as described above is used as the fuel.However, when the ratio of the citric acid that is the fuel is slightlylarger, since a combustion reaction is smooth to improve physicalproperties of the manufactured ceramic powder, it is preferable toincrease the ratio of the citric acid. The increase amount is changedaccording to the composition of the synthesized perovskite.

Next, it is preferable that a particle diameter of lanthanum cobaltitethat is another starting raw material be 0.5 to 5.0 μm and lanthanumcobaltite be dense and spherical powder where there is no pore betweenprimary particles.

The spherical lanthanum cobaltite powder is manufactured by mixinglanthanum oxides and cobalt oxides, heating the mixture at thetemperature of 1400° C. or more for 5 hours or more to performsynthesis, and pulverizing the mixture.

A method of forming a precursor by using cellulose and combusting theprecursor may be used as another method of manufacturing lanthanumcobaltite powder. Examples of another method of manufacturing lanthanumcobaltite powder include a method of dissolving metal chlorides, citricacid and ethylene glycol in water to form an aqueous solution, removingwater and an organic material by heating, and performing heat treatmentat 400° C. or more.

Examples of another method of manufacturing lanthanum cobaltite powderinclude a method of manufacturing lanthanum cobaltite powder by drying aprecipitate produced by adding sodium hydroxide to lanthanum nitrate andthe cobalt nitrate aqueous solution and calcining the precipitate in theair at 700° C. for 6 hours. Examples of another method of manufacturinglanthanum cobaltite powder include a method of manufacturing lanthanumcobaltite powder by forming lanthanum nitrate and a cobalt nitrateaqueous solution, uniformly mixing lanthanum nitrate and the cobaltnitrate aqueous solution with a mixture of an acrylamide monomer and N,N′-methylenebiacrylamide, adding ammonium persulfate thereto to form agel, and performing heating.

It is preferable that the particle diameter of the lanthanum cobaltitepowder synthesized by the method selected from the aforementionedmanufacturing methods be 0.5 to 5.0 μm. If the particle diameter issmaller than 0.5 μm, after the powder is heat treated at 1400° C. ormore to grow the lanthanum cobaltite particles, the powder may bepulverized and then used.

However, in the case where the particle diameter is less than 0.5 μm, ahigh cost is required to manufacture the lanthanum cobaltite powder,which is not economical. Further, in the case where the particlediameter thereof is more than 5 μm, sintering required for the ceramicmaterial is interrupted, thus resultantly negatively affecting shrinkageratio and electrical conductivity.

This effect is confirmed by a method of adding lanthanum cobaltite to bedescribed below and a change in shrinkage ratio and electricalconductivity according to the addition ratio thereof.

Since lanthanum cobaltite is not substantially sintered at 700 to 900°C. that is an operation temperature of the solid electrolyte fuel cell,if the particle diameter thereof is excessively large or the additionratio is excessively high, shrinkage ratio and electrical conductivityof the composite ceramic material are reduced.

In addition, it is preferable that the addition ratio of lanthanumcobaltite be selected to be 10 wt % or more and 90 wt % or less in thefinally obtained composite ceramic material. In the case where theaddition ratio of lanthanum cobaltite is less than 10 wt %, an improvingeffect of conductivity is small, and in the case where the additionratio is more than 90%, since the ceramic material is not sintered atthe operation temperature of the solid oxide fuel cell, strength issignificantly reduced, and as a result, the ceramic material may beeasily broken.

Hereinafter, a method for manufacturing the composite ceramic materialaccording to the exemplary embodiment of the present invention will bedescribed.

First, the nitrate aqueous solution is manufactured by the followingmethod. Nitrates such as lanthanum nitrate, calcium nitrate, chromenitrate, cobalt nitrate and copper nitrate are weighed to correspond toa stoichiometric composition of the ABO₃ perovskite ceramic, added todistilled water to be dissolved therein, agitated at low temperatures,and heated. Further, the prepared lanthanum cobaltite powder is added tothe prepared citric acid (citric acid monohydrate), uniformly mixedtherewith, and then added to the nitrate aqueous solution to performsolation.

The mixed solution of the sol state is gelated by slowly being heated toincrease viscosity, and continuously heated until agitation cannot beperformed.

Thereafter, if the heating temperature is further increased to finishgel bubbling and form a viscous cake state, heating is performed to theself-ignition temperature of the solidified gel or more so that the gelis self-ignited to be combusted, and cooling is performed.

After the chars manufactured as described above are dry-pulverized andthen clacined in the air at 700° C. or more. In this case, it ispreferable that the calcining temperature be 700° C. or more that is atemperature at which a perovskite single phase is confirmed through anX-ray diffraction analysis and 1000° C. or less that is a temperature atwhich calcined powder is not sintered.

The shape of the calcined powder is a shape where the perovskite ceramicparticles finally formed by the nitrate aqueous solution surround thelanthanum cobaltite particles having a particle diameter that is largerthan that of the perovskite ceramic particles. This structure is calleda cored structure.

In this case, it is preferable that the particle diameter of lanthanumcobaltite be 0.5 to 5.0 μm and the particle diameter of the perovskiteceramic particles synthesized together to surround the lanthanumcobaltite particles be 100 nm or less.

It is preferable that the aforementioned cored structure be maintainedeven though a subsequent physical process such as ball-milling isperformed.

The calcined powder was put into a plastic jar together with ethanol anda zirconia ball, ball-milled, dried, and distributed.

The calcined powder manufactured by the aforementioned method isuniformly mixed by adding a combining material, dried, shaped, andsintered while being in contact with both sides of the electrode plateand the separation plate of the solid oxide fuel cell to be used as thecomposite ceramic material.

In this case, it is preferable that the sintering condition be 600° C.or more and 1 hour or more. If the sintering temperature is lower than600° C., strength of a sintered body is not sufficient, such that thesintered body is broken and a function of a contact material is lost. Ifthe temperature is higher than the aforementioned temperature range, thetemperature is advantageous with respect to strength shrinkage of theceramic material, but damage to other constituent elements constitutingthe fuel cell, for example the metal separation plate or the glasssealing material, is increased.

That is, if the ceramic material of the present invention is sintered at600° C. or more that is the operation temperature range of the solidoxide fuel cell for 1 hour or more, a function thereof is exhibited. Inthe case where the temperature is increased as compared to the sinteringtemperature or a sintering time is increased, a microstructure of theceramic material may be denser.

The manufactured calcined powder may be uniformly mixed together with anappropriate combining material, dispersion material, solvent and thelike to obtain a viscous fluid (slurry) form, extruded in a linear stateor a surface state on the solid oxide fuel cell single cell (unit cell)or the separation plate (interconnect), and sinter-attached to be usedas the ceramic material.

As another use example, a paste is manufactured by mixing themanufactured calcining powder with an organic combining agent and adispersing agent, applied on the solid oxide fuel cell separation plate,dried, sintered, and attached to the separation plate to be used as theceramic material.

Hereinafter, Examples of the present invention will be described indetail.

Example 1

First, lanthanum cobaltite was synthesized as one of starting materials.

To this end, lanthanum oxide and cobalt oxide were mixed, and heated atthe temperature of 1400° C. for 5 hours or more to synthesize lanthanumcobaltite. The synthesized lanthanum cobaltite was pulverized to form apowder state. The manufactured powder of lanthanum cobaltite wasmanufactured to have a dense and spherical shape without pores betweenprimary particles as shown in the picture taken by the scanning electronmicroscope (SEM) of FIG. 1. The average particle diameter of themanufactured lanthanum cobaltite was about 3 μm.

Next, the nitrate aqueous solution was manufactured. The composition ofthe nitrate aqueous solution was adjusted by weighing and mixingnitrates so that the composition of the finally formed perovskiteceramic was (La,Ca) (Cr,Co,Cu)O₃ (hereinafter, referred to as ‘LCCAF’).The accurate composition of LCCAF used in the present Example was(La_(0.8)Ca_(0.2))(Cr_(0.1)Co_(0.6)Cu_(0.3))O₃.

76.9 g of lanthanum nitrate, 10.4 g of calcium nitrate, 8.9 g of chromenitrate, 38.5 g of cobalt nitrate, and 16.0 g of copper nitrate wereadded to 50 mL of distilled water in order to manufacture the nitrateaqueous solution having the aforementioned composition, completelydissolved therein, and heated to 70° C. while being agitated.

Thereafter, 50.0 g of the lanthanum cobaltite powder manufactured thuslywas added to 85.0 g of the citric acid (citric acid monohydrate) that ispowder at room temperature and uniformly mixed, and the mixture was thenadded to the nitrate aqueous solution.

The mixed solution in the aforementioned state was continuously heatedat 70° C. until it was impossible to perform agitation because of theincreased viscosity. Thereafter, the heating temperature was increasedto 150° C. to finish gel bubbling and form a viscous cake state. If thecake state was formed, the gel solidified by heating the cake to 250° C.or more was self-ignited to be combusted, and the char was obtained bycooling the combusted gel. The char thusly obtained was dry-pulverizedin the ball mill. Thereafter, the char was dried, heated at thetemperature increase speed of 2° C./min, and clacined in the air at 700°C. for 4 hours.

The powder synthesized by the aforementioned method was shown in FIG. 2.

As seen from FIG. 2, the composite powder obtained by synthesizing thenitrate aqueous solution and the lanthanum cobaltite particles have ashape where small particles surround large particles. This structure iscalled a cored structure. The particle having the large particlediameter is lanthanum cobaltite and the particle diameter thereof is 2to 5 μm, and the particles having the small particle diameter are LCCAFand the particle diameter thereof is about 50 nm.

It is preferable that the aforementioned cored structure be maintainedeven though a subsequent physical process such as ball-milling isperformed. Accordingly, in the case where the calcined particles areball-milled, it is necessary to control a ball-mill process so that theagglomerated LCCAF particles are pulverized to be uniformly dispersedaround the lanthanum cobaltite particles.

The calcined powder was put into the plastic jar together with ethanoland the zirconia ball, ball-milled for 15 hours, and dried at 60° C. for24 hours or more. The dried powder was distributed into the size of 150μm or less.

The sample where lanthanum cobaltite was simply mixed with the LCCAFsynthetic powder separately synthesized by using the nitrate aqueoussolution and the citric acid was prepared in order to compare physicalproperties of the synthetic ceramic calcined powder manufactured by theaforementioned process. Hereinafter, the powder synthesized to have thecored structure according to the exemplary embodiment of the presentinvention is called “synthetic powder”, and the powder obtained bysimply mixing LCCAF powder synthesized by a separate process andlanthanum cobaltite is called “mixed powder”.

Samples that are synthesized or mixed by changing the addition ratio oflanthanum cobaltite to the final ceramic powder to 10 to 90 wt % werecalcined under the same condition in order to compare physicalproperties of the synthetic powder and the mixed powder. The calciningconditions of the powders were all 700° C. and 12 hours. The calcinedpowder was mixed with an organic binder through pulverizing, shaped, andsintered. In this case, the sintering condition is 850° C. and 4 hours.

The following Table 1 shows results obtained measuring sinteringshrinkage of the sintering process with respect to the aforementionedexperiment condition and the sintered body and electrical conductivityat 800° C. that is the operation temperature range of the solid oxidefuel cell. In this case, after the sintered sample was processed intoprism having a size of 3*3*20 (mm), electrical conductivity thereof wasmeasured at 800° C. by the four-probe method.

TABLE 1 Lanthanum cobaltite ratio (wt %) 10 30 50 70 90 Synthetic MixedSynthetic Mixed Synthetic Mixed Synthetic Mixed Synthetic MixedClassification powder powder powder powder powder powder powder powderpowder powder Shrinkage (%) 8.9 5.8 16.6 10.9 14.4 10.9 6.4 4.3 2.5 1.3Electrical 111.8 75.5 192.1 101.5 228.4 180.5 117.2 94.2 100.2 88.3conductivity (S/cm)

As shown in Table 1, it can be seen that in the case of the syntheticpowder, sintering shrinkage and electrical conductivity are higher thanthose of the mixed powder. Accordingly, the synthetic powder accordingto the exemplary embodiment of the present invention has excellentsintering property and electrical conductivity as compared to the mixedpowder.

The experimental results mean that since the sintering property of thesynthetic powder according to the present invention is significantlyimproved, in the case where the synthetic powder is used as a contactmaterial in the separation plate of the solid oxide fuel cell, a densenetwork structure can be maintained.

Further, the synthetic powder according to the present inventionimproves a flow of electrons at a contact point of the lanthanumcobaltite particles to reduce electrical resistance of the ceramicmaterial, as a result, the total electrical conductivity of the fuelcell stack is improved.

Example 2

In Example 2, the amount of synthetic powder manufactured according toExample 1 was increased to be 250 g in one batch, and physicalproperties with pure LCCAF powder were compared. (The amount ofsynthetic powder synthesized in Example 1 is 100 g in one batch.)

First, pure LCCAF powder was synthesized by adding only the citric acidto the nitrate aqueous solution weighed in a stoichiometric composition.In addition, synthetic powder was synthesized by the same method asExample 1 for the purpose of comparison therewith. In this case, thecomposition of lanthanum cobaltite in synthetic powder was set so thatthe ratio of lanthanum cobaltite in powder obtained after calcining was50 wt %. Hereinafter, synthesized LCCAF powder is called “pure LCCAFpowder”, and synthetic powder synthesized for comparison is called “50%synthetic powder”.

The powders synthesized as described above were shaped into disks havingthe diameter of 25 mm by each adding 1.0 wt % of polyvinylbutyral andperforming uniaxial pressing to 1,000 kgf/cm². The shaped bodies weresintered in the air at 850° C. for 4 hours. In this case, the shrinkagewas measured during sintering. In addition, the sintered body wasprocessed into prism having the size of 3*3*20 (mm), and electricalconductivity was then measured by the four-probe method at 800° C.

Shrinkage and electrical conductivity during sintering were 16.2% and64.3 S/cm, respectively, in the case of pure LCCAF powder, and 18.6% and505.2 S/cm, respectively, in the case of 50% synthetic powder.

Since lanthanum cobaltite powder was not substantially sintered at 800°C., sintering shrinkage of synthetic powder including 50 wt % oflanthanum cobaltite powder was lower than sintering shrinkage of pureLCCAF. However, since electrical conductivity is increased by fourtimes, sintering shrinkage is reduced by 1.8% point, thus compensating areduction effect of electrical conductivity.

Example 3

In Example 3, synthetic powder manufactured according to Example 2 wasapplied as a contact material to the separation plate of the solid oxidefuel cell, and electric characteristics of the fuel cell were examined.

The sample used in this experiment is 50% synthetic powder synthesizedaccording to Example 2.

Synthesized 50% synthetic powder, the organic combining material, thedispersion material and the solvent were mixed with each other tomanufacture the slurry.

This slurry was put into the syringe-shaped container, and applied in alinear form on the solid oxide fuel cell separation plate by using adispenser device. Further, this was sintered in the air at 850° C. for 4hours.

In the used solid oxide fuel cell, the single cell was formed ofLaSrCoFeO₃ (LSCF) anode, yttria stabilized zirconia (YSZ), and Ni—YSZcathode, the separation plate was formed of a stainless steel material(ferritic steel), and the sealing material was glass.

In this case, while the current collector formed between the separationplate and the anode was changed, a current voltage characteristic of thefuel cell was examined.

The used current collectors were compared with respect to the threecases of use of 1) a ceramic material manufactured according to Example3, 2) a contact material formed of a platinum mesh (Pt mesh) and aplatinum paste (Pt paste) and 3) a metal mesh manufactured by theferritic steel-based stainless alloy and electroplated with Co—Ni.

With respect to the three types of fuel cells, the examination resultsof current-voltage characteristics are shown in FIG. 3.

As seen from FIG. 3, it can be seen that the solid oxide fuel cellusing 1) the ceramic material manufactured according to Example 3 hasthe same or higher electric characteristic as compared to the case where2) the platinum mesh and the platinum paste are used.

However, as compared to the case where the metal current collector of 3)is used, the metal current collector of 3) exhibits performance of about94% as compared to 1) the ceramic material manufactured according toExample 3. Accordingly, in the case where 2) the platinum mesh and theplatinum paste are used, costly platinum is used, but in the case of 1)the ceramic material, since performance is the same and the cost is low,the ceramic material is advantageous in view of industrialapplicability.

Example 4

In Example 4, the mixed powder having the same composition as “50%synthetic powder” of Example 2, that is, powder manufactured by simplymixing separate LCCAF powder and lanthanum cobaltite, was sintered, andsintering shrinkage and electrical conductivity thereof were compared.

To this end, in the mixed powder, after pure LCCAF powder wasmanufactured in a separate process, lanthanum cobaltite powder wasweighed and simply mixed therewith so that the ratio was 50 wt %.(hereinafter, referred to as “50% mixed powder”)

Each powder prepared thusly was mixed with 1 wt % of polyvinylbutyral,ball-milled, and dried. Thereafter, shaping and sintering were performedby the same procedure as Example 2, and shrinkage and electricalconductivity were measured.

As a result, shrinkage and electrical conductivity of 50% syntheticpowder were 18.6% and 505.2 S/cm and shrinkage and electricalconductivity of 50% mixed powder were measured to be 10.9% and 180.5S/cm, respectively.

As described above, shrinkage and electrical conductivity of 50% mixedpowder were lower than those of 50% synthetic powder. The results showthat there is a large difference in physical properties according to asynthetic state thereof rather than the composition ratio of LCCAFpowder and lanthanum cobaltite powder. This result can be confirmed inthe aforementioned Table 1.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A composite ceramic material comprising: fine ABO₃ type perovskiteceramic particles compositely synthesized with lanthanum cobaltite(LaCoO₃) particles having a particle diameter that is larger than aparticle diameter of the perovskite ceramic particle.
 2. The compositeceramic material of claim 1, wherein: a ratio of the lanthanum cobaltiteis greater than 10 wt % and less than 90 wt %.
 3. The composite ceramicmaterial of claim 1, wherein: the perovskite ceramic particle is any oneof (La,Sr)MnO₃, (La,Sr)CoO₃, (La,Sr) (Co,Fe)O₃, and (La,Ca)(Cr,Co,Cu)O₃.
 4. The composite ceramic material of claim 1, wherein: aparticle diameter of the lanthanum cobaltite particle is 0.5 to 5.0 μm.5. The composite ceramic material of claim 1, wherein: the lanthanumcobaltite particle has a sphere shape.
 6. The composite ceramic materialof claim 1, wherein: a particle diameter of the perovskite ceramicparticle is 100 nm or less.
 7. The composite ceramic material of claim1, wherein: a cored structure where the perovskite ceramic particlessurround the lanthanum cobaltite particles is formed.
 8. The compositeceramic material of claim 1, wherein: the lanthanum cobaltite issynthesized by being added with a starting material in a process ofsynthesizing the perovskite ceramic particles.
 9. The composite ceramicmaterial of claim 1, wherein: a composition of the perovskite ceramic is(La_(0.8)Ca_(0.2))(Cr_(0.1)Co_(0.6)Cu_(0.3))O₃.
 10. A method ofmanufacturing a composite ceramic material, comprising: adding a mixturewhere citric acid and lanthanum cobaltite powder are mixed with eachother to a nitrate aqueous solution where a plurality of nitrates aredissolved; heating and agitating the aqueous solution to convert areactant from a sol state to a gel state; heating the reactant producedin the heating and agitating to a temperature of a self-ignition or moreof the citric acid to combust the citric acid; and pulverizing charsproduced in the combusting the citric acid and then calcining the charsat 700° C. or more.
 11. The method of manufacturing a composite ceramicmaterial of claim 10, wherein: a particle diameter of the lanthanumcobaltite powder is 0.5 to 5.0 μm.
 12. The method of manufacturing acomposite ceramic material of claim 10, wherein: the nitrate aqueoussolution is obtained by dissolving at least one metal nitrate selectedfrom lanthanum nitrate, calcium nitrate, chrome nitrate, cobalt nitrate,copper nitrate, iron nitrate, bismuth nitrate, yttrium nitrate,manganese nitrate, strontium nitrate and nickel nitrate in distilledwater to correspond to a composition of a ABO₃ perovskite ceramic. 13.The method of manufacturing a composite ceramic material of claim 10,wherein: a ratio of the lanthanum cobaltite added to the nitrate aqueoussolution is greater than 10 wt % and less than 90 wt %.
 14. The methodof manufacturing a composite ceramic material of claim 13, wherein: theABO₃ perovskite ceramic is any one of (La,Sr)MnO₃, (La,Sr)CoO₃, (La,Sr)(Co,Fe)O₃, and (La,Ca) (Cr,Co,Cu)O₃.
 15. The method of manufacturing acomposite ceramic material of claim 14, wherein: a composition of the(La,Ca) (Cr,Co,Cu)O₃ is (La_(0.8)Ca_(0.2))(Cr_(0.1)Co_(0.6)Cu_(0.3))O₃.16. The method of manufacturing a composite ceramic material of claim10, wherein: the citric acid is a combustible organic materialcontributing to forming a metal complex and forming ceramic powder bycombustion at high temperatures.
 17. The method of manufacturing acomposite ceramic material of claim 16, wherein: the combustible organicmaterial is any one of glycine nitrate, polyethylene glycol, urea andethylenediamine tetraacetate.
 18. The method of manufacturing acomposite ceramic material of claim 10, further comprising: uniformlymixing powder calcined in the calcining, a combining material, adispersion material and a solvent to manufacture a viscous fluid(slurry).
 19. The method of manufacturing a composite ceramic materialof claim 18, further comprising: applying the viscous fluid on a polarplate or a separation plate of a fuel cell and then sintering theviscous fluid.
 20. The method of manufacturing a composite ceramicmaterial of claim 19, wherein: the sintering is performed at 600° C. ormore for 1 hour or more.